#include "apue.h"

static volatile sig_atomic_t sigflag;
static sigset_t newmask, oldmask, zeromask;

static void sig_usr(int signo) {
	sigflag = 1;
}

void 
TELL_WAIT(void) {
	if (signal(SIGUSR1, sig_usr) == SIG_ERR) {
		err_sys("signal(SIGUSR1) error");
	}

	if (signal(SIGUSR2, sig_usr) == SIG_ERR) {
		err_sys("signal(SIGUSR2) error");
	}

	sigemptyset(&zeromask);
	sigemptyset(&newmask);
	sigaddset(&newmask, SIGUSR1);
	sigaddset(&newmask, SIGUSR2);

	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0) {
		err_sys("SIG_BLOCK error");
	}
}

void 
TELL_PARENT(pid_t pid) {
	kill(pid, SIGUSR2);
}

void 
WAIT_PARENT(void) {
	while (sigflag == 0) {
		sigsuspend(&zeromask);
	}

	sigflag = 0;

	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0) {
		err_sys("SIG_SETMASK error");
	}
}

void 
TELL_CHILD(pid_t pid) {
	kill(pid, SIGUSR1);
}

void 
WAIT_CHILD(void) {
	while (sigflag == 0) {
		sigsuspend(&zeromask);
	}

	sigflag = 0;

	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0) {
		err_sys("SIG_SETMASK error");
	}
}

int 
main(void) {
	pid_t pid;

	if ((pid = fork()) < 0) {
		err_sys("fork error");
	} else if (pid == 0) {
		printf("child running\n");

		sleep(5);

		printf("child done\n");

		TELL_PARENT(getppid());
	} else {
		TELL_WAIT();	

		printf("parent running\n");

		WAIT_CHILD();
		
		printf("parent done\n");
	}
	
	exit(0);
}
